Initial commit: notification-elements-ui library

Angular 19 component library for notifications & communication:
- ntf-bell: notification bell with badge count and shake animation
- ntf-feed / ntf-feed-item: real-time notification feed with grouping
- ntf-center: full notification center with category filter tabs
- ntf-inbox / ntf-inbox-item: two-column inbox with search and detail
- ntf-comment / ntf-thread: comment threads with replies and reactions
- ntf-mention-input: text input with @mention autocomplete
- ntf-empty-state: empty state placeholder
- ntf-item-def: custom template directive for notification items

Includes signal-based services, SCSS design tokens with dark mode,
utility functions, and full TypeScript type definitions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/services/notification.service.ts

@@ -0,0 +1,56 @@
+import { Injectable, inject, signal, computed } from '@angular/core';
+import { NOTIFICATION_CONFIG } from '../providers/notification-config.provider';
+import type { NtfNotification, NtfGroup } from '../types/notification.types';
+import { groupByDate } from '../utils/time.utils';
+
+@Injectable()
+export class NotificationService {
+  private config = inject(NOTIFICATION_CONFIG);
+
+  readonly notifications = signal<NtfNotification[]>([]);
+
+  readonly unreadCount = computed(() =>
+    this.notifications().filter((n) => n.status === 'unread').length,
+  );
+
+  readonly grouped = computed<NtfGroup[]>(() => {
+    const items = this.notifications().filter((n) => n.status !== 'archived');
+    const dateGroups = groupByDate(items);
+
+    return dateGroups.map((g) => ({
+      id: g.label.toLowerCase().replace(/\s+/g, '-'),
+      label: g.label,
+      notifications: g.items,
+    }));
+  });
+
+  add(notification: NtfNotification): void {
+    this.notifications.update((list) => [notification, ...list]);
+  }
+
+  markRead(notificationId: string): void {
+    this.notifications.update((list) =>
+      list.map((n) => (n.id === notificationId ? { ...n, status: 'read' as const } : n)),
+    );
+  }
+
+  markAllRead(): void {
+    this.notifications.update((list) =>
+      list.map((n) => (n.status === 'unread' ? { ...n, status: 'read' as const } : n)),
+    );
+  }
+
+  archive(notificationId: string): void {
+    this.notifications.update((list) =>
+      list.map((n) => (n.id === notificationId ? { ...n, status: 'archived' as const } : n)),
+    );
+  }
+
+  remove(notificationId: string): void {
+    this.notifications.update((list) => list.filter((n) => n.id !== notificationId));
+  }
+
+  clear(): void {
+    this.notifications.set([]);
+  }
+}